The present invention relates to a novel titanyl phthalocyanine crystal formed from a titanyl phthalocyanine compound. The present invention also relates to a method of producing the titanyl phthalocyanine crystal. The present invention also relates to an electrophotosensitive material using the titanyl phthalocyanine crystal as an electric charge generating material. The present invention further relates to a method of producing the electrophotosensitive material.
Electrophotosensitive materials are used in image forming apparatuses such as electrostatic copying machine, laser printer and plain paper facsimile.
As the electrophotosensitive material, a so-called organic photosensitive material formed by using the following components in combination has widely been used.
Electric charge generating material which are irradiated with light to generate electric charges (holes and electrons).
Electric charge transferring material for transferring the generated electric charges, which is classified into a hole transferring material for transferring holes and an electron transferring material for transferring electrons.
Binding resin having a film forming property.
The organic photosensitive material has such an advantage that it is easily produced as compared with an inorganic photosensitive material using an inorganic semiconductor material.
The organic photosensitive material also has advantages such as wide range of choice of materials such as electric charge generating material, electric charge transferring material and binding resin, and high functional design freedom.
The organic photosensitive material is produced by forming a single-layer or multi-layer type photosensitive material on a conductive substrate.
The single-layer type photosensitive layer is formed by dispersing an electric charge generating material in a binding resin, together with an electric charge transferring material (hole transferring material and/or electron transferring material).
The multi-layer type photosensitive layer is formed by laminating an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material (hole transferring material or electron transferring material) in this order or a reverse order.
As the electric charge generating material, for example, various pigments can be used according to the sensitivity range of the photosensitive material.
As the electric charge generating material for photosensitive material which is sensitive to infrared or near infrared light emitted from a semiconductor laser or infrared LED, for example, phthalocyanine pigments have widely been used.
The phthalocyanine pigment varies depending on the chemical structure and includes, for example, metal-free phthalocyanine compound, copper phthalocyanine and titanyl phthalocyanine. The respective compounds can be in various crystal forms.
Therefore, crystals having various crystal forms of various phthalocyanine compounds have been studied by a lot of investigators to find out optimum crystals suited best for use as the electric charge generating material.
For example, Japanese Patent No. 2907121 discloses that a crystal having a Y type crystal form of titanyl phthalocyanine is superior in sensitivity characteristics for electric charge generating material to a crystal having the other crystal form and can contribute to an improvement in sensitivity of the electrophotosensitive material.
A coating solution for the single-layer type photosensitive layer, or a coating solution for electric charge generating layer of the multi-layer type photosensitive layer using the Y type titanyl phthalocyanine crystal can be prepared by adding the crystal and other components in an organic solvent and uniformly dispersing them.
The layer formed by coating the coating solution on the substrate immediately after preparation or within about 60 minutes, and drying the coating solution is particularly superior in sensitivity characteristics as described in the above publication.
As is apparent from the present inventors"" study, the sensitivity characteristics of the layer, which was formed by coating the coating solution after storage for a fixed time (e.g. 24 hours) and drying the coating solution, is drastically lowered as compared with the layer formed by using the coating solution immediately after preparation.
It has been found that, since the coating solution prepared by using the Y type titanyl phthalocyanine crystal described in the above publication is inferior in storage stability, the photosensitive layer having good sensitivity characteristics can not be formed stably.
A main object of the present invention is to provide a novel titanyl phthalocyanine crystal capable of preparing a coating solution having excellent storage stability, which can stably form a photosensitive layer having good sensitivity characteristics.
Another object of the present invention is to provide a method of producing the titanyl phthalocyanine crystal.
Still another object of the present invention is to provide an electrophotosensitive material having excellent sensitivity characteristics using the titanyl phthalocyanine crystal, and a method of producing the same.
To attain the objects described above, the present inventors has studied about the cause of deterioration of the storage stability using a conventional Y type titanyl phthalocyanine crystal described above. As a result, they have found the following fact.
A conventional Y type titanyl phthalocyanine crystal has poor stability in an organic solvent contained in the coating solution, for example, tetrahydrofuran. Therefore, a crystal transfer is liable to occur, that is, the Y type crystal form is gradually changed into the xcex2 type crystal with poor sensitivity characteristics during the storage of the coating solution in a fixed period. Therefore, the longer the lapsed time after preparation, the inferior the sensitivity characteristics of the layer formed by using such a coating solution tend to become.
Therefore, the present inventors have studied about the physical properties to improve the stability of the titanyl phthalocyanine in the organic solvent.
As a result, they have found that the titanyl phthalocyanine crystal satisfying at least one of the following two physical properties (a) and (b) is superior in stability in the organic solvent to a conventional Y type titanyl phthalocyanine crystal and hardly causes crystal form changing, as is apparent from the results of the Examples and Comparative Examples described below, so that a coating solution having excellent storage stability can be formed. Thus, the present invention has been completed.
(a) The crystal does not have a peak of a change in temperature within a range from 50 to 400xc2x0 C. except for a peak associated with evaporation of adsorbed water in differential scanning calorimetry.
(b) The crystal recovered after dipping in an organic solvent for 24 hours has at least a maximum peak at a Bragg angle 2xcex8xc2x10.2xc2x0=27.2xc2x0 and has no peak at 26.2xc2x0 in a CuK xcex1 characteristic X-ray diffraction spectrum.
The titanyl phthalocyanine crystal of the present invention can be produced by the production method of the present invention, which comprises the following steps:
a pigmentation pretreatment step of adding a titanyl phthalocyanine in an aqueous organic solvent, stirring under heating for a fixed time, and allowing the resulting solution to stand for a fixed time under the conditions at a temperature lower than that of the above stirring process, thereby to stabilize the solution; and
a pigmentation step of removing the aqueous organic solvent from the solution to obtain a crude crystal of the titanyl phthalocyanine, dissolving the crude crystal in a solvent, adding dropwise the solution in a poor solvent to recrystallize the titanyl phthalocyanine compound, and then subjecting the recrystallized compound to milling treatment in a non-aqueous solvent in the presence of water.
The titanyl phthalocyanine crystal of the present invention can be produced by other production methods which comprise the following steps:
a pigmentation pretreatment step of adding a titanyl phthalocyanine in an aqueous organic solvent, stirring under heating for a fixed time, and allowing the resulting solution to stand for a fixed time under the conditions at a temperature lower than that of the above stirring process, thereby to stabilize the solution;
a step of removing the aqueous organic solvent from the solution to obtain a crude crystal of the titanyl phthalocyanine, and treating the crude crystal according to acid-paste method; and
a step of subjecting a low-crystalline titanyl phthalocyanine compound obtained by the above steps to milling treatment, with water contained therein.
The electrophotosensitive material of the present invention comprises a photosensitive layer containing the titanyl phthalocyanine crystal of the present invention as the electric charge generating material.
Examples of the photosensitive layer include:
(A) a single-layer type photosensitive layer containing the titanyl phthalocyanine crystal and at least one of a hole transferring material and an electron transferring material in a binding resin; and
(B) a multi-layer type photosensitive layer comprising an electric charge generating layer containing the titanyl phthalocyanine crystal and an electric charge transferring layer containing one of a hole transferring material and an electron transferring material, which are mutually laminated.
The electrophotosensitive material of the present invention can attain good sensitivity characteristics, that are always stable regardless of the lapsed time after preparing the coating solution.
The titanyl phthalocyanine crystal of the present invention can retain a crystal form stably in the photosensitive layer even after preparing the photosensitive material. Therefore, the photosensitive material can retain good sensitivity characteristics, that are stable with a lapse of time, without lowering the sensitivity characteristics on use.
Another photosensitive material of the present invention is characterized in that the titanyl phthalocyanine crystal recovered after isolating from the photosensitive layer and dipping in tetrahydrofuran for 24 hours under the conditions of a temperature of 23xc2x11xc2x0 C. and a relative humidity of 50 to 60% has at least a maximum peak at a Bragg angle 2xcex8xc2x10.2xc2x0=27.2xc2x0 and an intensity of a peak at 26.2xc2x0 does not exceed the intensity of the maximum peak in a CuK xcex1 characteristic X-ray diffraction spectrum.
Further, according to the production method of the present invention, which comprises the following steps, it is possible to produce an electrophotosensitive material comprising said single-layer type or multi-layer type photosensitive layer, which attains good sensitivity characteristics that are always stable regardless of the lapsed time after preparing a coating solution.
(Single-layer Type)
A step of preparing a coating solution by adding a titanyl phthalocyanine crystal and other components in an organic solvent, and
a step of forming a single-layer type photosensitive layer by coating the coating solution, followed by drying.
(Multi-layer Type)
A step of preparing a coating solution by adding a titanyl phthalocyanine crystal and a binding resin in an organic solvent, and
a step of forming an electric charge generating layer by coating the coating solution, followed by drying.